Weird graphical glitches caused by 2d batching

[MightyPrinny]

Godot version:
3.3.1 Mono

OS/device including version:
MXLinux 19/Debian 10 64bits, GLES2

Issue description:
I'm not sure what's going on exaclty, but I was able to replicate part of the glitches I was seeing in a project,

glitch.mp4

Here things are disappearing, I was also seeing things being drawn at an offset in a project.

Steps to reproduce:
In the reproduction project I had to use different zindex, a script with custom 2d drawing and a grid lines shader.
It might be worth noting that the draw code uses global coordinates.

func _draw():
	if(texture == null):
		return;
	#global_position = referencePosition;
	draw_set_transform(-global_position,0,Vector2.ONE);
	
	var dir:Vector2 = (global_position-Vector2(0,16)-referencePosition).normalized();
	for i in range(length):
		draw_texture(texture,referencePosition+Vector2(-8,16)+i*16*dir);

Minimal reproduction project:
DrawGlitch.zip

[lawnjelly]

Am just taking a look.

Turned out to be due to a state getting stale in the batching and not being updated. It was probably a very rare bug but nice to have fixed, it was probably only working in most cases by chance.

Given that the test project is quite complex, it is possible there is more than 1 bug. I spent some time isolating and identifying this one, and the test project seems to be working ok for me now. Let me know if you spot any other problems in the project once the fix is merged.

[akien-mga]

Fixed by #48992.